Wireless communication networks are widely deployed to provide various communication services such as telephony, video, data, messaging, broadcasts, and so on. Such networks, which are usually multiple access networks, support communications for multiple users by sharing the available network resources.
In a wireless communication network, roaming is a term used where a mobile station visits a network that is not its home PLMN (public land mobile network). The visited network is frequently referred to as a VPLMN (V being visited). The visited network may or may not belong to the same country as the home PLMN.
The identity of a network is generally provided by PLMN ID. A PLMN ID generally includes a combination of a mobile country code (MCC) and a mobile network code (MNC). The GSMA maintains a definitive list of PLMN IDs used worldwide, where each 3GPP-compliant mobile network is identified by its MCC and MNC. Each cell in such a mobile network broadcasts its MCC and MNC so that a mobile station can identify which network it is in. Generally, each country utilizes one (or in some cases, more than one) country code, and many countries typically have several networks and therefore several MNCs. Within a MCC, each mobile network has a unique MNC.
When a mobile station is roaming, that is, when it is registered on a VPLMN, it generally uses one of several algorithms to periodically search for its home PLMN. This is because although the mobile station is registered on the best cell according to signal characteristics, if the mobile station is nearby its home PLMN, e.g., near a border, for various reasons including the increased charges to the user for voice or data calls, it would be preferable for the mobile station to register on its home PLMN. For example, the mobile may search for its home PLMN at regular, fixed intervals, or it may search at longer and longer intervals over time, as it comes to determine that the success of the search is less likely as it continues to fail.
Searching for the home PLMN while registered on a VPLMN generally includes processes such as measuring the power received on all the supported frequencies/bands to establish an available cell list, and reading the identity of each cell to determine its PLMN ID until the home PLMN ID is found or the available cell list is exhausted. These processes consume a considerable amount of power. Thus, each time the mobile searches for the home PLMN, power consumption at the mobile is increased, particularly when the mobile is in an idle or standby mode.
However, when the home PLMN is not in the vicinity of the VPLMN serving the mobile station, there may be little to no possibility that the search processes would find the home PLMN. For example, a mobile station having a home network in the United States, when registered on a network in Australia, would necessarily fail in a search for its home PLMN. Thus, such a search for the home PLMN in this scenario would be a waste of power that would be advantageous to avoid.
Others have attempted to address this issue by configuring the network to transmit information to the mobile station whether the VPLMN is within the vicinity of the mobile station's HPLMN. Here, if the VPLMN is not in the vicinity of the HPLMN, scanning and searching for the HPLMN may be eliminated. For example, Ericsson published a document titled, “Border problem and efficient periodic search,” presented at 3GPP TSG-CN-WG1, Meeting #17. In this document, Ericsson disclosed a procedure of transmitting a neighbor PLMN list using signaling mechanisms (i.e., via broadcast messages, registration messages, or LA/RA updates). However, this solution required transmission of the neighbor PLMN list to the mobile station at the demand of the network, rather than the mobile station; and further, by requiring transmission from the network, required changes to the standards that define communication over the air interface.
As the demand for mobile broadband access continues to increase, research and development continue to advance the wireless technologies not only to meet the growing demand for mobile broadband access, but to advance and enhance the user experience with mobile communications.